From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EBA43EBF3B for ; Wed, 18 Mar 2026 18:45:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773859524; cv=none; b=DaJz9Dyw9qw6aOnVMNI61R180lCGnuP63McyfLIL53d+HsQEjncPtiBVScVv4YwV3tOF3QEM6D0qzGDSzmfSEdRwk3bI8FRl9YMlhzfCbqoSL6IPLy3QTkTw1onOiwlAK2cCF+Fdxfn9oLLFKFh4Tfz0MmMFFX+yzIdIF0pzeb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773859524; c=relaxed/simple; bh=lx4a4VCvtwpGXczIyJApAGWYUAMSzJfW6I61mZV8Xk8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HnO60AEvK3czwzupyX8b74U1ZG4rri2qS/OPSD74fRVt8pvITWn77/bNuIQy7Z3inqfze1Ms8fbRaReyQnxmJ0xQy1EZxxcftv1UQBFG9u3HNZiywXjg4LNC+2MKGKeKW6Tb7aJ5WIWFXoZ15tg2H7V3UafrTJt2e8fYzxcc2y0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lBzr2Spb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lBzr2Spb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 82BF0C2BC9E; Wed, 18 Mar 2026 18:45:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773859523; bh=lx4a4VCvtwpGXczIyJApAGWYUAMSzJfW6I61mZV8Xk8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=lBzr2SpbyG8Fg0Q0XCHqPxP2bCZu7gOej9vSItLLo43hYNLwBngZYY1Z4z/a5Dvqd uO6E0+USM3PXwN9CWqhJiqCUViQmgq+N33P3qk5buXbduXcscx5q+f9OybQnZ8jGJM Mjj48/LXlQpuA95SfVPtSuTERq0Yt9o7rVNIvXjKT1LpKaehmLmvZam+/+HaDu4GCL NsCVQ8dSsCmpwUwF6BDbSYJtVZWzhlkAhyr9brDUINlMlLBEMNm7Us/+ulYdcfL76p 2+O0p409ZK97NOLpd6ew/bttE219RVtgj3eH7BiIFO1Cg2scJIe6pgHphMyOTB/71n xzNXHflwtblJQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 545E6CE098B; Wed, 18 Mar 2026 11:45:21 -0700 (PDT) Date: Wed, 18 Mar 2026 11:45:21 -0700 From: "Paul E. McKenney" To: Boqun Feng Cc: Sebastian Andrzej Siewior , frederic@kernel.org, neeraj.iitr10@gmail.com, urezki@gmail.com, joelagnelf@nvidia.com, boqun.feng@gmail.com, rcu@vger.kernel.org, Kumar Kartikeya Dwivedi Subject: Re: Next-level bug in SRCU implementation of RCU Tasks Trace + PREEMPT_RT Message-ID: <0f0fa46f-4d41-4e79-a6be-46b832c6ae65@paulmck-laptop> Reply-To: paulmck@kernel.org References: <20260318105058.j2aKncBU@linutronix.de> <20260318144305.xI6RDtzk@linutronix.de> <76ef9a5e-7343-4b8e-bf3c-cabd8753ecdb@paulmck-laptop> <20260318160445.IyUiWV0T@linutronix.de> <06a0cb91-1737-4691-a810-8340e1acf1d6@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Mar 18, 2026 at 09:42:09AM -0700, Boqun Feng wrote: > On Wed, Mar 18, 2026 at 09:32:07AM -0700, Paul E. McKenney wrote: > > On Wed, Mar 18, 2026 at 05:04:45PM +0100, Sebastian Andrzej Siewior wrote: > > > On 2026-03-18 08:43:32 [-0700], Paul E. McKenney wrote: > > > > > Your patch just s/spinlock_t/raw_spinlock_t so we get the locking/ > > > > > nesting right. The wakeup problem remains, right? > > > > > But looking at the code, there is just srcu_funnel_gp_start(). If its > > > > > srcu_schedule_cbs_sdp() / queue_delayed_work() usage is always delayed > > > > > then there will be always a timer and never a direct wake up of the > > > > > worker. Wouldn't that work? > > > > > > > > Right, that patch fixes one lockdep problem, but another remains. > > > > > > What remains? > > > > With that patch, we no longer have call_srcu() directly acquiring a > > non-raw spinlock, but as you say, we still have the wakeup problem. > > I don't think we have a wakeup problem since we use workqueue to defer > the wakeup, but maybe I'm missing something here? You are right, I was confused. We instead have a deadlock problem. Thanx, Paul